Audio and video signals are processed in many applications to obtain a desired phase shift. For example, some implementations of multichannel audio matrix coding use a variety of filtering techniques to impart a ninety-degree phase shift in so-called surround channels so that a matrix can combine the surround channels with the left and right front channels in a way that preserves the relative energy or power of the left and right channels. This improves the fidelity of playback systems that do not have a matrix decoder but instead playback the matrixed left and right channels.
Known filtering techniques for obtaining a ninety-degree phase shift have limitations and disadvantages. Some of the filtering techniques used with multichannel audio matrix coding apply a filter to both the surround channels as well as the front channels to obtain a relative phase shift of ninety-degrees between these channels. Preferably, the phase shift should be obtained without shifting the phase of the front channels. Other techniques use finite impulse response (FIR) filters to approximate the non-causal infinite impulse response of the Hilbert transform; however, these FIR implementations are computationally intensive and must truncate the infinite impulse response. As a result, these FIR implementations can only approximate the response with limited accuracy and must tradeoff the degree of accuracy with the computational efficiency.